Radio frequency identification (RFID) is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency (RF) portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. RFID is coming into increasing use in industry as an alternative to the bar code. The advantage of RFID is that it does not require direct contact or line-of-sight scanning. RFID is sometimes also called dedicated short range communication (DSRC).
In an RFID system multiple wireless tags are interrogated by sending information from an interrogating transmitter to the tags and having information transmitted by the tag in response. This is commonly accomplished by having the tag listen for an interrogation and for it to respond with a unique serial number and/or other information. However, it is desirable to extend the range of wireless tags so that it is not necessary to bring each tag close to a reader for reading. Three problems are evident when extending the range of the reading system. One of the problems is that there is limited power available for transmission from the wireless tag. Two, if the range is significant, it is possible that many tags will be within range of the interrogating system and their replies may corrupt each other. And, three, tag power supply levels will vary during their dialog with readers and may even be frequently interrupted entirely for periods up to one second.
RFID tags can be used to identify items. And, as outlined, there are known methods that enable one specific tag in a group of many tags to be interrogated without corruption by other tags of information sent by that one particular tag to the reader and without accidental transmission of data or commands to other tags of information sent to that particular tag.
The least expensive tags usually have EEPROM or read only memory. This is adequate for identifying a tag and for executing a purchase. However, at times, the purchaser might require privacy after the purchase so that another party cannot perform a scan and learn the contents of that purchaser's purse, car or home.
Thus, there are times when it is desirable to permanently disable or destroy an RFID tag after purchase. Furthermore, when a tag is destroyed it is desirable that other tags within range of the disabling device, typically a reader, are not also destroyed.
Although there are times when it would be desirable to intentionally and selectively destroy a tag so that it is no longer possible to read the information encoded on that tag, at the same time, it is also important to not create an opportunity for theft.
It would also be desirable to keep the cost of a tag and peripheral equipment to a minimum, and to enable rapid interrogation of a tag. One means of achieving these goals is in using short code lengths, for example 8 bits. However, an eight bit code has only 256 possible permutations and its protective effect can be circumvented by use of various electronic devices. It would therefore also be desirable to inhibit the use of electronic means that rapidly transmit all permutations of a code in order to circumvent a device's security.
Likewise, it is also important that certain tag states like the SLEEP/WAKE or other command states persist even through short interruptions of the power supply.